Last Week on My Mac: Increasingly insecure in Sequoia

Over the last nine years, few of my articles here have been about XProtect, other than those announcing its updates. Until September 2024 and the release of macOS 15 Sequoia. This is now the tenth article I have written about the problems brought by XProtect updates in Sequoia over those six months, when there have been just 13 updates. The result of the last, on 4 March, was that for two days afterwards, many Macs running Sequoia were still using its data from 26 February rather than that in the new version 5289.

This not only affects XProtect, but the other front-line tool in macOS to detect and remove malicious software, XProtect Remediator (XPR). Earlier this year, I reported that at least 17 of the 24 scanning modules in XPR now use Yara definitions provided by XProtect’s data. All those Macs still running the superseded version of XProtect would also have had XPR scans run using that old version of the Yara rules.

XPR is a recent addition to these tools, introduced just three years ago, but XProtect goes way back before Yosemite in 2014. Although there have been occasional brief glitches in delivery of its updates, they have almost invariably completed quickly and reliably, leaving very few Macs stuck with an outdated version 24 hours after an update.

I have now come to dread XProtect updates because of the problems we encounter, and the latest update to 5289 was a good example. There’s a flurry of comments and emails from those whose Macs had failed to complete the update, previously a rare exception. For XProtect 5287 on 5 February, for example, there were 33, including my responses. For version 2184 exactly a year earlier there’s not one comment about that XProtect update.

Sole documentation provided about XProtect’s updates in Sequoia is the man file for its command tool, xprotect, which refers only to updates provided via iCloud, and doesn’t explain how those delivered via the traditional mechanism in softwareupdate might be involved. Yet we know there is a relation: the latest update has still not been supplied via iCloud, not even four days later, but relied instead on XProtectUpdateService working with an update obtained via softwareupdate. Previously that could be invoked using the xprotect update command, but that no longer works, leaving users with two versions of XProtect data, of which the copy used by XProtect and XPR is the older.

Late last year, when xprotect update appeared to be working as expected, I decided that my app SilentKnight would need to use that command in order to download and install updates. As that requires elevated privileges, I have been looking at how to implement a privileged helper app to perform that. With the latest update, that approach would have failed until the version in iCloud had been brought up to date. Instead we’re now reduced to restarting our Macs and hoping that, some time in the next day or two, they might update.

There’s a further problem emerging with the updates of 4 March. Many users have noticed subsequent XPR scans being terminated before completion. Although in most cases that fault appears to go away in later scans, in some Macs it prematurely terminates every set of XPR scans, leaving several of its scanning modules unused.

For example, this iMac Pro has failed to scan using ten of its 24 modules. This occurs because XPR apparently runs a timer, and when a round of scans is deemed to be taking too long, that timer fires and brings XPR to an abrupt halt. Indications are this is most likely when there are many Time Machine backups accessible; as those are all immutable snapshots and haven’t changed since they were made months ago, this is strange behaviour, and hadn’t occurred prior to the updates of 4 March.

Six months ago, if anyone had told me that macOS security protection in Sequoia was going to become less reliable, I wouldn’t have believed them. The truth is that, for many, it now has. As things stand in 15.3.1, a Mac is now more likely to be using an out of date version of XProtect’s detection rules, and for XPR scans to detect and remove malware. And there’s nothing you can do about that until Apple returns to using an update mechanism that’s both timely and reliable. Is that really too much to expect of this front-line security protection?

Selected previous articles:

What is happening with XProtect updates?
XProtect tormentor
How XProtect has changed in macOS Sequoia
A simple guide to how XProtect installs and updates in Sequoia
XProtect has changed again in macOS Sequoia 15.2
What happened with XProtect?
What has happened to XProtect in Sequoia?